Method and system for implementing aggregate endpoints on IMS networks

ABSTRACT

A method and system are adapted to provide telephony services to aggregate endpoints on an Internet Protocol Multimedia Subsystem (IMS) network. The method includes assigning one or multiple PUIDs for surrogate registration purposes during the provisioning of the aggregate endpoint, performing reliable surrogate registration on behalf of the aggregate endpoint, allowing multiple SBCs to perform surrogate registrations independently for the same aggregate endpoint to achieve reliability, and providing reliable connection from an IMS core to the aggregate endpoints via multiple S/BCs. The system includes one or more Session Border Controllers (S/BC), at least one set of Call/Session Control Functions (CSCF), and an HSS operatively coupled together.

STATEMENT OF JOINT DEVELOPMENT AGREEMENT

The present invention was made under the auspices of joint developmentagreement to which AT&T Corporation, Alcatel-Lucent Corporation, andAcme Packet Corporation, are parties.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention generally relates to providing Internet Protocol(IP) telephony services to a collection of users behind aggregateendpoints that connect to a network, such as business customer sites orwholesale customer sites. Examples of IP telephony services include theEP Multimedia Subsystem (IMS), as well as other services in which userendpoints are required to register to the network in order to receivereliable service.

2. Brief Description of the Related Art

In the Internet Protocol (IP) Multimedia Subsystem (IMS) standard, whichwas originally designed for the individual subscriber wireless networksand is incorporated herein by reference, all subscribers need toregister first before they can obtain services from the IMS network. Asdefined in the 3^(rd) Generation Partnership Program (3GPP) IMS standardfor, IMS network service providers use a Public User Identity (PUID) asthe identifier to recognize the subscriber. The PUID is included in aP-Asserted-Identity (PAI) header in Session Initiation Protocol (SIP)INVITE messages for outbound calls, Request-URI header in SIP Invitemessages for inbound calls, and the To header in SIP registrationmessages.

As service providers increasingly offer services to aggregate orcollections of users or subscribers, such as business and wholesalecustomers, using the same IMS network that provides reliable services toindividual subscribers, the following key issues arise:

-   -   1. Customer Premise Equipment (CPE) devices for business or        wholesale customer equipment do not register with the (IMS)        network. Examples of some endpoints that cannot register are:        -   (a) legacy Time Division Multiplexing (TDM) Public Branch            Exchanges (PBXs) that access an IP network through a            Voice-Over-IP (VoIP) gateway;        -   (b) an IP device at customer premises that can not perform            registration, such as IP PBX, or CPE running            teleconferencing application; and in some cases, the PBX is            a stateful proxy serving local IP phones, it usually is also            their Registrar and thus will not forward the phone            Registers on to the Core; and        -   (c) wholesale equipment access to the IMS network via            routers.    -   2. Business or wholesale services are applied to the connection        or group instead of the individual subscriber. For example,        based on a wholesale access point connection to the service        provider, the wholesale service needs to be invoked as the        originating service treatment for call screening, blocking, and        routing.

SUMMARY OF THE INVENTION

A method of providing telephony services to aggregate endpoints on anInternet Protocol Multimedia Subsystem (IMS) network in accordance withone form of the present invention, which incorporates some of thepreferred features, includes assigning a Public User Identity (PUID) toan aggregate endpoint by one or more Session Border Controllers forsurrogate registration purposes, and performing reliable surrogateregistration on behalf of the aggregate endpoint via one or multipleSession Border Controllers (S/BC). The aggregate endpoint may be abusiness customer site or a wholesale customer site.

The method also includes identifying an aggregate endpoint to beregistered, and performing surrogate registration on behalf of theaggregate endpoint. The surrogate registration is not performed by theaggregate endpoint, and the surrogate registration is not performed bythe plurality of user devices obtaining telephony services through theaggregate endpoint. The surrogate registration is preferably performedby at least one Session Border Controller (S/BC). Surrogate registrationmay be performed by a plurality of Session Border Controllers (S/BC)that may be adapted to independently perform surrogate registration onbehalf of the aggregate endpoint. At least one of a Public User Identity(PUID) and a Private User Identity (PRID) associated with the aggregateendpoint may be stored in the Session Border Controller (S/BC), and thePrivate User Identity (PRID) may include a group identification (ID)associated with the aggregate endpoint.

A system adapted to provide telephony services to aggregate endpoint onan IMS network in accordance with one form of the present invention,which incorporates some of the preferred features, includes one or moreSession Border Controller (S/BC) operatively coupled to the aggregateendpoint, at least one set of Call/Session Control Functions (CSCF)operatively coupled to the S/BC, and an HSS operatively coupled to theCSCFs. A PUID or multiple PUIDs for surrogate registration purpose canbe assigned to the aggregate endpoint, and at least one of the S/BC,CSCF, and HSS identifies the aggregate endpoint during the provisioningof telephony services to the aggregate endpoint.

The surrogate registration is performed on behalf of the aggregateendpoint. The surrogate registration is not performed by the aggregateendpoint, and is not performed by the plurality of user devicesobtaining telephony services through the aggregate endpoint. Surrogateregistration is preferably performed by the at least one Session BorderController (S/BC), and may be performed by a plurality of Session BorderControllers (S/BC) adapted to independently perform surrogateregistration on behalf of the aggregate endpoint. The Session BorderController (S/BC) may store at least one of a Public User Identity(PUID) and a Private User Identity (PRID) associated with the aggregateendpoint, and the Private User Identity (PRID) may include a groupidentification (ID) associated with the aggregate endpoint.

A computer-readable medium comprising instructions, wherein execution ofthe instructions by at least one processing device causes telephonyservices to be provided to aggregate endpoint on an IMS network byassigning the PUID to an aggregate endpoint associated with a pluralityof users obtaining telephony services through the aggregate endpoint,and identifying the aggregate endpoint using the surrogate registeredPUID during the provisioning of telephony services. The steps mayinclude assigning a PUID to the aggregate endpoint, performing reliablesurrogate registration on behalf of the aggregate endpoint, and allowingmultiple SBCs to perform surrogate registration independently for thesame aggregate endpoint to achieve reliability. The steps includeidentifying an aggregate endpoint to be registered, and performingsurrogate registration on behalf of the aggregate endpoint. Thesurrogate registration is not performed by the aggregate endpoint, andis not performed by the plurality of user devices obtaining telephonyservices through the aggregate endpoint.

Other objects and features of the present invention will become apparentfrom the following detailed description considered in conjunction withthe accompanying drawings. It is to be understood, however, that thedrawings are designed as an illustration only and not as a definition ofthe limits of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram that shows a business customer access.

FIG. 2 is a block diagram that shows a wholesale customer access.

FIG. 3 is a block diagram showing surrogate registration of an aggregateendpoint, such as a business customer site or a wholesale customer site,in an Internet Protocol (IP) Multimedia Subsystem (IMS) network inaccordance with the present invention.

FIG. 4 is a block diagram showing propagation of an outbound call fromthe aggregate endpoint in the IMS network in accordance with the presentinvention.

FIG. 5 is a block diagram showing propagation of an inbound call to theaggregate endpoint in the IMS network in accordance with the presentinvention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

As shown in FIG. 1, business enterprise customers are customers thataccess the network, such as an IMS core 11 using a Private BranchExchange (PBX) 13 or switch (TDM or softswitch). As shown in FIG. 2,wholesale customers are preferably a network 15 that resells services oraccess to the service provider 17. Thus, services are provided based onthe access point for that network, and not typically on a per subscriber19, 21 basis. For such customers, identification information regardingspecific individual users obtaining services through the business orwholesale customer is not known, nor does it need to be known inaccordance with the present invention. This type of access point isreferred to herein as an “aggregate endpoint”. The actual users 19, 21behind the aggregate endpoint are connected to the network via one ormore Session Border Controllers (S/BC) 10, but are not consideredindividual subscribers.

The present invention is directed to make one or more Session BorderControllers (S/BC) 10 performing surrogate registration on behalf of theaggregate endpoints. The S/BC 10 preferably uses a PUID recognized bythe IMS network, to identify the originating aggregate endpoint, and totrigger the originating or terminating services.

Identification

Regarding the identification of a business customer or a wholesalecustomer, each business/wholesale customer location (access) isconsidered as an aggregate endpoint and allocated a private useridentity, and a public user identity for surrogate registrationpurposes. The user device or phone associated with or behind theaggregate endpoint is preferably assigned the PUIDs that would be usedfor call originating and call terminating.

Provisioning

When a customer order comes in, a PUID for surrogate registration ispreferably assigned to the aggregate endpoint. The PUID for surrogateregistration will be provisioned in one or more S/BCs and a HomeSubscriber Server (HSS).

After provisioning, the S/BC will contain Public User Identity (PUID)and Private User ID (PRID) information for the aggregate endpoint, whichrepresents a collection of users. The PUID for surrogate registration ispreferably a group ID, which is assigned to the aggregate endpoint forthe purpose of surrogate registration. The HSS contains the user profilefor the aggregate endpoint. There are also some other PUIDs which arethe phones behind the aggregate endpoint that will be used to originatecalls from or terminate calls to. Those PUIDs will be provisioned in theHSS as part of the implicit registration set along with the PUID for thesurrogate registration.

An example of the provisioned data in the HSS and S/BC used in theexample call flow shown in FIG. 3 is as follows:

-   -   “id.example_ims.net” is the home network domain name;    -   “cust1_site1_prid@id.example_ims.net” is the Private User        Identity for an aggregate endpoint (a business/wholesale        customer in one location);    -   “cust1_site1@id.example_ims.net” is the Public User Identity        used for implicit registration of an aggregate endpoint (a        business/wholesale customer in one location); and    -   “+19876541000@ id.example_ims.net”, . . . “sip:+19876542000@        id.example_ims.net” are the PUIDs in the implicit registration        set that will be registered via the surrogate registration        process.        Surrogate Registration of an Aggregate Endpoint

The IMS standard is defined with the concept that a user is registeredto the IMS core so that the user can initiate and receive calls from thenetwork. To allow an aggregate endpoint to interface with an IMSnetwork, the aggregate endpoint must be registered with the network.Registration may rely on standard IMS registration procedures based onthe private and public user identities representing thebusiness/wholesale customer site as a whole.

FIG. 3 shows an example of the preferred registration call flow inaccordance with the present invention. Blocks 10-16 represent functionsimplemented in software and/or hardware. When an aggregate endpointconnects to the IMS network for the first time, one or more SessionBorder Controllers (S/BC) 10, which function as a firewall or accesspoint to the network, preferably perform surrogate registration onbehalf of the business customer's Customer Premise Equipment (CPE) 18 orwholesale customer's equipment 20 since these customers are unable toperform this function.

In addition, HSS 24 contains the PRID and PUID for the aggregateendpoint and the service profile associated with the aggregate endpoint.This information is downloaded to the S-CSCF 16 for future callprocessing during the registration.

The detailed Registration call flow preferably proceeds as follows:

-   -   1. S/BC 10 sends Register message 22 to Proxy Call/Session        Control Function (P-CSCF) 12. The Register message includes:        -   the aggregate endpoint's (in this case, business customer 18            or wholesale customer 20) Public User Identity (PUID)            (cust1_site1@id.example_ims.net) in the SIP From header and            To header;        -   the aggregate endpoint's Private User Identity (PRID)            (cust1_site1_prid@id.example_ims.net) in the SIP            Authorization header.    -   2. Upon receiving the SIP Register message from S/BC 10, P-CSCF        12 proxies the SIP Register message to Interrogating        Call/Session Control Function (I-CSCF) 14.    -   3. I-CSCF 14 contacts Home Subscriber Server (HSS) 22 via the        Diameter User-Authorization-Request (UAR) message to determine        if there is a Serving Call/Session Control Function (S-CSCF) 16        already allocated to the PUID cust1_site1@id.example_ims.net.    -   4. HSS 22 responds with Diameter User-Authorization-Answer (UAA)        message to I-CSCF 14 that provides the S-CSCF's capability        information.    -   5. I-CSCF 14 performs the S-CSCF selection based on the        capabilities received from HSS 22 and forwards the SIP Register        message to S-CSCF 16    -   6. S-CSCF 16 sends a 401 Unauthorized message to I-CSCF 14.    -   7. I-CSCF 14 proxies the 401 Unauthorized message to P-CSCF 12.    -   8. P-CSCF 12 proxies the 401 Unauthorized message to S/BC 10.    -   9. S/BC 10 computes credentials for the registration and sends a        new Register message with credentials to the P-CSCF 12. The        difference between the new Register message and the Register        message in Step 1 is that the credentials are included in the        Authorization header.    -   10. P-CSCF 12 proxies a Register message with credentials to        I-CSCF 14.    -   11. I-CSCF 14 sends the Diameter UAR message to the HSS 24 to        determine if there is an S-CSCF already allocated to PUID        cust1_site1@id.example_ims.net.    -   12. HSS 24 responds with Diameter UAA message to I-CSCF 14 with        S-CSCF 16's information.    -   13. I-CSCF 14 proxies the Register message with credentials to        S-CSCF 16.    -   14. Upon receiving the Register message, the S-CSCF 16 performs        Diameter Multimedia-Auth-Request (MAR) message to HSS 24 to        download the authentication data for PUID        cust1_site1@id.example_ims.net.    -   15. The HSS 24 stores the S-CSCF 16 URI for PUID        cust1_site1@id.example_ims.net and answers with Diameter        Multimedia-Auth-Answer (MAA) message with the authentication        data (authentication vectors).    -   16. The S-CSCF 16 validates the credentials against the        authentication vector. The authentication is successful.    -   17. The S-CSCF 16 then sends the Diameter        Server-Assignment-Request (SAR) message to the HSS to inform the        PUID cust1_site1@id.example_ims.net has registered and starts to        download the service profile for this user.    -   18. The HSS 24 responds with Diameter Server-Assignment-Answer        (SAA) message, which includes the service profile for PUID        cust1_site1@id.example_ims.net. The service profile includes all        the Initial Filter Criteria (iFC) required for this customer.        Since this is an implicit registration, the service profile        includes all the Public User Identities in the implicit        registration set for the aggregate endpoint (business customer        18 or wholesale customer 20).    -   19. The S-CSCF 16 sends a 200 OK to the I-CSCF 14 that includes        all the Public User Identities registered from this implicit        registration process in the P-Associated-URI header. A        service-route header will be included to indicate the S-CSCF 16.        An example of a P-Associated-URI header in a 200 OK message is        as follows:        -   P-Associated-URI:        -   <sip:cust1_site1@id.example_ims.net>,        -   <sip:+19876541000@ id.example_ims.net>,        -   . . .        -   <sip:+19876542000@ id.example_ims.net>    -   20. The I-CSCF 14 proxies the 200 OK message to P-CSCF 16.    -   21. The P-CSCF 16 proxies the 200 OK message to S/BC 10. At the        same time, P-CSCF 16 stores the PUID information to be used for        the future call setup.    -   22. Now all users behind the aggregate endpoint are registered        using PUID cust1_site1@id.example_ims.net.        It is to be noted that if multiple S/BCs perform the surrogate        registration on behalf of an aggregate endpoint, the last        registration is the one in effect.

It is to be noted that the PUID described herein makes use of theimplicit registration concept. This enables the aggregate endpoint toselect and provide one or more numbers as the implicit registered PUIDsto be used to call the aggregate endpoint. As defined by IMS, implicitregistration is functionally equivalent to a User Endpoint or userdevice (UE) explicitly registering each Address of Record (AoR) in termsof access and routing support, except that the explicit registration ofone AoR (public-id) triggers the implicit registration of all the otherAoRs (public-ids) associated with that UE. The implicitly registeredAoRs are passed back to the UE in the 200 ok of the Registration, asP-Associated-URIs. For example, assume the aggregate endpoint is a bankwith a PBX connection. The PUID is used to access one or more numbersthat can be used to actually reach the bank, such as 1-987-654-1000 and1-987-654-2000 shown in the HSS data block 30 in FIG. 3, so that afterthe registration, all these implicit registered numbers can be reached.

Following registration of the aggregate endpoint, calls associated withthat aggregate endpoint will be permitted to pass through the S/BC 10into the network. In some cases, if a single registration cannotimplicitly register all the phone numbers off the aggregate endpoints,multiple, separately provisioned independent surrogate registrations canbe performed.

As a summary, key characteristics of the registration include:

-   -   1. S/BC 10 uses surrogate registration method used for        individual customer to register on behalf of aggregate endpoint        using a provisioned group ID as the PUID for surrogate        registration purpose.    -   2. One or more S/BC would perform the same registration on        behalf of a common set of PUIDs for the aggregate endpoint. The        last that performed surrogate registration would be the one that        is in effect.    -   3. If a single registration cannot implicitly register all the        phone numbers off the aggregate endpoints, multiple, separately        provisioned independent surrogate registrations can be        performed.    -   4. As a result of surrogate registration, all the PUIDs in the        implicit registration set are registered. The implicit        registered PUIDs are contained in the P-Associated-URI header in        the 200 OK message.    -   5. The Proxy Call/Session Control Function (P-CSCF) and S-CSCF        that handles the registration preferably stores the PUID and the        Contact information for the aggregate endpoint for future call        setup verification.    -   6. This step preferably repeats whenever the new registration or        re-registration occurs, such as S/BC 10 restarts or the        registration timer expires.        Calls, Originating from an Aggregate Endpoint

When an aggregate endpoint makes a call, an outbound call will belaunched from the Customer Premise Equipment (CPE) to one of the S/BCs.FIG. 4 shows an example of an outbound call flow.

After registration, the HSS 24 has already downloaded the profile of theaggregate endpoint to the S-CSCF, which enables the AS 32 to betriggered so that the specific services requested by the aggregateendpoint may be provided. The AS 32 handles particular functions, suchas call forwarding, conferencing, and call waiting, which are subscribedto by the particular aggregate endpoint. The following detailed examplecall flow describes the preferred procedure to invoke originating ASprocessing:

-   1. S/BC 10 receives a SIP INVITE request from an aggregate endpoint    (Business CPE 18 or Wholesale equipment 20). The INVITE preferably    includes:    -   a Calling Party Number in the From Header; and    -   a Dialed number in the R-URI and To Header.-   2. S/BC 10 forwards the SIP INVITE 34 to the P-CSCF 12.-   3. P-CSCF 12 verifies the customer, generates P-Asserted-Identity    header based on the SIP FROM header, and forwards the INVITE to the    S-CSCF 16.-   4. Using the PUID carried in the P-Asserted-Identity header, the    S-CSCF checks the filter criteria for the request using the Service    Point Triggers received in the request. From the service filter    criteria (PUID/PAI/Domain/IP address is used as the trigger in this    case), S-CSCF 16 determines if there are originating services that    apply to this call. If there is no originating service that applies    to this call, proceed to step 8.-   5. If there are originating services that apply to the call, the    S-CSCF forwards the request to AS 32 which has the highest priority.-   6. When AS 32 receives the request, it invokes the service logic and    performs service processing.-   7. Depending on the service needs, the AS 32 will act as a stateful    proxy, a stateless proxy, redirect server or a Back-to-Back User    Agent. The AS 32 will construct SIP Request-URI based on the    information the AS 32 received and the customer provisioned data in    AS 32. Then the AS 32 forwards the request to the S-CSCF 16.-   8. When the S-CSCF 16 receives the SIP INVITE from the AS 32, the    SCSF 16 checks the list of the services that apply to this call.    -   If there are other originating services that applies to this        call, proceed to Step 5.    -   If there is no other originating service that applies to this        call, the S-CSCF 16 will route the call by using ENUM/DNS query        (for SIP URI) query. If there is a positive response, the S-CSCF        16 will forward the request to I-CSCF in the terminating        network. If there is a negative response, the S-CSCF 16 will        forward the request to the BGCF.

Some key characteristics for the call setup are:

-   -   a. When an aggregate endpoint initiates a call, it can route the        calls to one or more S/BCs which have performed registration on        behalf of the aggregate endpoint. To achieve the goals of        reliability and load sharing, multiple S/BCs are preferably        used,    -   b. The PUID contained in the SIP FROM header sent by the        aggregate endpoint is the implicit registered PUID stated in the        surrogate registration section.        Calls Terminating to the Aggregate Endpoint

Similar to the standard inbound calls to an implicit registered endpointdefined in 3GPP, for the calls terminating to an aggregate endpoint, theE.164 number is preferably used to reach the aggregate endpoint. Thepreferred termination call flow is shown in FIG. 5. The E.164numbers+19876541000 and +19876542000 are used and preferably registeredduring the surrogate registration implicit registration processdescribed above. The general inbound call flow is shown by arrow 38.

-   -   1. The I-CSCF 14 receives the SIP INVITE from the originating        S-CSCF or MGCF. The I-CSCF 14 exchanges the Diameter        Location-Info-Request (LIR)/Location-Info-Answer (LIA) with the        HSS 24 to determine the S-CSCF for the called party (Request        URI), one of the PUIDs from the implicit registration set. After        the determination, I-CSCF 14 forwards SIP INVITE 40 to the        S-CSCF 16 for the terminating party.    -   2. Upon receiving SIP INVITE from I-CSCF 14, the S-CSCF 16 first        identifies the called party by the R-URI (a PUID in the implicit        registration set) in the INVITE message. Then, the S-CSCF        applies the initial filter criteria (iFC) in the user profile        for the called party. If there is no service that needs to be        invoked, proceed to Step 7.    -   3. The S-CSCF 16 determines that there is a set of services that        needs to be invoked. Based on the priority defined in the iFC,        the service with the highest priority will be invoked. The        S-CSCF 16 forwards the SIP INVITE to the AS 32.    -   4. Upon receiving the SIP INVITE request, the AS 32 accesses the        customer record and performs service processing.    -   5. Depending on the service, the AS 32 will either act as a SIP        stateful proxy, redirect server, or a Back-to-Back User Agent.        The AS 32 forwards the SIP INVITE request to the S-CSCF 16.    -   6. Upon receiving the SIP INVITE from AS 32, the S-CSCF 16        checks if additional AS processing is needed. If yes, proceed to        step 3.    -   7. When the S-CSCF 16 finds there are no other services to be        invoked, S-CSCF 16 sets the Request-URI to the contact address        of S/BC 10 and proxies the INVITE with SDP to the P-CSCF 12.    -   8. The P-CSCF 12 queries the DNS, and based on the DNS response,        it routes the INVITE to S/BC 10    -   9. The S/BC selects the customer site and sends an appropriate        SIP INVITE with SDP to the aggregate endpoint site (Business CPE        18).

The inbound call flow preferably uses substantially the similarprocedures defined in the 3GPP standard for terminating calls to animplicit registered endpoint. It is to be noted that using a Domain NameServer (DNS) query to reach S/BC in step 8 would allow inbound trafficload sharing among multiple S/BCs. This would help to achieve thereliability/load sharing goal for inbound traffic.

Thus, with limited vendor development, this invention solves theproblems in conventional approaches by using existing technologies. Inthis way, IMS service providers can offer services to business andwholesale customers without sacrificing their service needs.

Although preferred embodiments of the present invention have beendescribed herein with reference to the accompanying drawings, it is tobe understood that the invention is not limited to those preciseembodiments and that various other changes and modifications may beaffected herein by one skilled in the art without departing from thescope or spirit of the invention, and that it is intended to claim allsuch changes and modifications that fall within the scope of theinvention.

What is claimed is:
 1. A method of providing telephony services to anaggregate endpoint on an internet protocol multimedia subsystem network,the method comprising: identifying an aggregate endpoint to beregistered, the aggregate endpoint being associated with a plurality ofuser devices, the plurality of user devices obtaining telephony servicesthrough the aggregate endpoint; performing surrogate registration onbehalf of the aggregate endpoint by one of a plurality of session bordercontrollers coupled to the aggregate endpoint, wherein a lastregistration performed on behalf of the aggregate endpoint remains ineffect until superseded by a subsequent surrogate registration; andstoring a public user identity and a private user identity of atelephony device associated with the aggregate endpoint in one of theplurality of session border controllers, the private user identitycomprising a group identification associated with the aggregateendpoint.
 2. The method of providing telephony services to an aggregateendpoint on an internet protocol multimedia subsystem network defined byclaim 1, further comprising performing surrogate registration by theplurality of session border controllers, each of the plurality ofsession border controllers being performing surrogate registration onbehalf of the aggregate endpoint.
 3. The method of providing telephonyservices to an aggregate endpoint on an internet protocol multimediasubsystem network defined by claim 1, wherein the aggregate endpointcomprises a business customer.
 4. A system that provides telephonyservices to an aggregate endpoint on an internet protocol multimediasubsystem network, the system comprising: a plurality of session bordercontrollers operatively coupled to the aggregate endpoint, the aggregateendpoint being associated with a plurality of user devices, theplurality of user devices obtaining telephony services through theaggregate endpoint; a call/session control function operatively coupledto one of the plurality of session border controllers; and a homesubscriber server operatively coupled to the call/session controlfunction, the surrogate registration being performed by one of theplurality of session border controllers on behalf of the aggregateendpoint, the surrogate registration not being performed by theplurality of user devices obtaining telephony services through theaggregate endpoint, wherein a last registration performed on behalf ofthe aggregate endpoint remains in effect until superseded by asubsequent surrogate registration, the one of the plurality of sessionborder controllers being operative to store a public user identity and aprivate user identity of a telephony device associated with theaggregate endpoint, the private user identity comprising a groupidentification associated with the aggregate endpoint.
 5. The systemthat provides telephony services to an aggregate endpoint on an internetprotocol multimedia subsystem network defined by claim 4, wherein eachof the plurality of session border controllers independently performssurrogate registration on behalf of the aggregate endpoint.
 6. Thesystem that provides telephony services to an aggregate endpoint on aninternet protocol multimedia subsystem network defined by claim 4,wherein the aggregate endpoint comprises a business customer.
 7. Thesystem that provides telephony services to an aggregate endpoint on aninternet protocol multimedia subsystem network defined by claim 4,wherein the public user identity comprises a group identificationassociated with the aggregate endpoint.
 8. A non-transitorycomputer-readable medium comprising instructions that, when executed bya processing device, cause telephony services to be provided to anaggregate endpoint associated with a plurality of user devices obtainingtelephony services through the aggregate endpoint on an internetprotocol multimedia subsystem network by performing operationscomprising: identifying an aggregate endpoint to be registered;performing surrogate registration on behalf of the aggregate endpoint byone of a plurality of session border controllers operatively coupled tothe aggregate endpoint, wherein a last registration performed on behalfof the aggregate endpoint remains in effect until superseded by asubsequent surrogate registration; and storing a public user identityand a private user identity of a telephony device associated with theaggregate endpoint in one of the plurality of session bordercontrollers, the private user identity comprising a group identificationassociated with the aggregate endpoint.
 9. The non-transitorycomputer-readable medium defined by claim 8, wherein, each of theplurality of session border controllers independently performs surrogateregistration on behalf of the aggregate endpoint.
 10. The non-transitorycomputer-readable medium defined by claim 8, wherein the aggregateendpoint comprises a business customer.
 11. The non-transitorycomputer-readable medium defined by claim 8, wherein the public useridentity comprises a group identification associated with the aggregateendpoint.
 12. The method of providing telephony services to an aggregateendpoint on an internet protocol multimedia subsystem network defined byclaim 1, wherein the aggregate endpoint comprises a wholesale customer.13. The system that provides telephony services to an aggregate endpointon an internet protocol multimedia subsystem network defined by claim 4,wherein the aggregate endpoint comprises a wholesale customer.
 14. Thenon-transitory computer-readable medium defined by claim 8, wherein theaggregate endpoint comprises a wholesale customer.